In a vehicle combination of a tractor vehicle (towing vehicle) and a trailing vehicle (towed vehicle) pressurized air and brake signals are supplied from the tractor vehicle to the trailing vehicle. Pneumatic brake systems comprising analog pressure signals generally use a trailer supply line for providing the pressurized air to the trailer pneumatic brake circuit and a trailer control line or trailer service line for transmitting the pneumatic control signals to the trailer pneumatic brake circuit. A tractor protection valve assembly is provided in the tractor vehicle to be connected with the trailer supply line and the trailer control line, which are realized as pipes. Thus the tractor protection valve assembly serves as an interface between the tractor vehicle and the trailing vehicle.
FIG. 10 depicts an electro-pneumatic brake system 1002 of a tractor vehicle according to the prior art. A primary reservoir 11 containing a primary supply pressure p11 and a secondary reservoir 12 containing a second supply pressure p12 are provided independently to supply the electro-pneumatic brake system 1002 with pressurized air, wherein p11 and p12 should be equal. The driver actuates the brake pedal 10, thereby actuating a dual brake valve 14 which transmits a primary driver's brake pressure p41 supplied by the primary reservoir 11, and a secondary driver's brake pressure p42 supplied by the secondary reservoir 12. The driver's brake pressures p41, p42 are analog pneumatic pressures conducted to brake circuits 2a, 2b, and 2c, which are a front axle brake circuit 2a and a rear axle brake circuit 2b of the tractor vehicle 1 and a trailer brake circuit 2c of the trailing vehicle 3.
In this brake system 1002 of the prior art the secondary brake driver's pressure p42 is delivered to the front axle brake circuit 2a, together with the secondary supply pressure p12, in order to enable brake processes at the front axle by the secondary reservoir 12. The primary brake pressure p41 and the primary supply pressure p11 are conducted to the rear axle brake circuit 2b in order to enable rear axle brake processes. Further ABS-valves 200 and 300 are provided in the front axle brake circuit 2a and the rear axle brake circuit 2b for ABS control, the ABS-valves each comprising two 2/2-solenoid valves, respectively. An electronic control unit (ECU) 6 controls the ABS-valves 200 and 300.
A tractor protection valve assembly (TPVA) 1008 is provided in the tractor vehicle 1 for supplying the trailer brake circuit 2c with trailer supply pressure p120 via a trailer supply line (trailer supply pipe) 120 and for transmitting a driver's brake pressure p121 (analog control pressure) via a trailer control line (service line) 121, both lines 120 and 121 being connected to the trailing vehicle 3.
The trailing vehicle 3 may comprise a separate ABS system, which is not depicted in FIG. 10; in this case the ECU 6 and an ABS-ECU of the trailer vehicle may be connected via an electronic data connection, which is not depicted in FIG. 10. The tractor protection valve assembly 1008 is merely pneumatic.
An external driver assistance system 5, for example cruise control (CC), adaptive cruise control (ACC) or a pre-crash system for preventing a crash or lowering the damage in case of a crash, outputs external brake requests XBR to the ECU 6; the ECU 6 receives the XBR signals and controls the ABS-valves 200 and 300 for realizing the external assistance function. Further, the ECU 6 itself may initiate assistance brake processes as part of a stability system like ESC (electronic stability control) for enhancing the driving stability of the tractor vehicle 1 by selectively actuating vehicle brakes of the rear axle brake circuit 2b or the front axle brake circuit 2a. External assistance brake processes demanded or requested by a further control unit and internal assistance brake functions of the ECU 6 itself are hereinafter called “assistance brake processes”; they are not initiated by the driver's brake pedal 10 and therefore they cannot be realized on basis of the driver's brake pressures p41 and p42. Further, some brake systems 1 include a trailer assistance control valve (TCV) to be actuated by a TCV handle to initiate an anti-Jackknife brake process for selectively actuating the trailer brakes but not the tractor vehicle brakes to “stretch” or align the vehicle combination. Such a driver induced trailer brake process without actuating the driver's brake pedal is also to be evaluated as an “assistance brake process”.
In order to execute assistance brake processes the ABS-valves 200 and 300 are charged with supply pressure p12 and p11, respectively, and controlled by the ECU 6 to deliver pressure values required for the assistance function.
Assistance brake processes can also be provided in the trailing vehicle. Therefore a trailer assistance control valve 250, which is configured in the same manner as the ABS valves 200 and 300, is switched between the front axle brake circuit 2a and the tractor protection valve 1008. Thus the ECU 6 outputs electric control signals to the trailer assistance control valve 250 in order to supply an analog pressure p250 as pneumatic control signal to the tractor protection valve assembly 1008, which in turn delivers the brake pressure p121 via the trailer control line 121 to start trailer brake processes. Thus the trailer assistance control valve 250 can be controlled in the same way as the ABS valves 200 and 300, in order to start assistance brake processes independently of the actuation of the brake pedal 10.
In general, it is better to connect the trailer assistance control valve 250 to the front axle brake circuit 2a rather than the rear axle brake circuit 2b, since additional control functions like a traction control systems for preventing a traction slip are provided at the driven rear axle; therefore the trailer assistance control valve 250 is separated from the rear axle brake circuit 2b. 
However, a piping extending from the front axle brake circuit 2a to the tractor protection valve (TPV) 1008 located at the backside of the tractor vehicle 1 is relatively long and therefore expensive; further, the pneumatic signals are delayed in such a long piping, and increasing and releasing the pressure in long pipings results in a high energy consumption.
An object of the invention is to provide a tractor protection valve assembly which enables assistance functions at low costs and low effort.
This object is realized by the tractor protection valve assembly according to claim 1. Further an electro-pneumatic brake system for a tractor vehicle comprising such a tractor protection valve is provided.
The tractor protection valve assembly according to the invention therefore comprises a single casing, in which at least one solenoid valve is provided. Further the supply inputs and outputs for receiving supply pressure as well as driver's control pressure and for supplying the trailing vehicle with supply pressure and control pressure are provided in the casing.
Thus an air piping between the front axle brake circuit and the tractor protection valve assembly is not necessary. Electric control signals supplied by the ECU are used for switching the at least one solenoid valve inside the tractor protection valve assembly, thereby using the pressure supply input for realizing assistance brake processes to be supplied to the trailer control pipe.
The invention provides several advantages:
The piping inside the tractor vehicle can be reduced. Thus the total equipment costs can be reduced, control functions are less delayed and energy consumption for pressure increase and release in the long pipings can be reduced.
The invention is based on the idea that a tractor protection valve assembly can be realized inside one casing by incorporating at least one, in particular one or two electrically controlled solenoid valves together with further pneumatic valve equipment like one or two two-way valves and a tractor protection valve (TPV), which tractor protection valve can in particular be realized as a pneumatically actuated 3/2 way valve.
The tractor protection valve is in particular pneumatically controlled by a trailer supply valve (TSV), which can be actuated by a TSV handle provided in the dashboard region of the tractor vehicle. The driver therefore actuates the TSV handle thereby pressurizing the trailer supply pipe in order to release the spring brakes of the trailing vehicle, thereby switching the TSV valve into its open status.
According to one embodiment two electrically controlled 2/2-solenoid valves are provided in the casing of the tractor protection valve assembly (TPVA), thereby enabling phases of pressure increase, pressure holding and pressure release (venting) in the trailer control line to be connected to the tractor protection valve assembly and plugged into an input of the trailer vehicle.
According to an alternative embodiment one electrically controlled 3/2 way solenoid valves is provided in the casing of the tractor protection valve assembly, thereby enabling phases of pressure increase and pressure release (venting) of the trailer control line extending to the trailer vehicle. Thus the phase “pressure holding” cannot be realized; however, the ECU may output control signals in order to alternatingly increase and release the control pressure output, leading to a pressure-time profile like a “sawtooth”. Such a sawtooth profile may increase the air consumption; however, it may reveal advantages, since it enables an ABS-like braking behavior of the trailer brakes.
The drawings are provided herewith for illustrative purposes only and are not intended to limit the scope of the present invention.